Geology (and other Earth Sciences)

http://www.csulb.edu/lats/itss/design/video/flash/geology/weaver/japan_killer_quake.html

Please Watch the video on the above link.
Why were parts of the coastline flooded by the 30-ft tsunami waves regardless of the 30-ft seawall?
Why were areas like Sendai flooded for several miles inland?
Why were cars found on top of buildings 8 meters high in an area hit by only 3-meter waves?
Generally speaking, what factors affected the height of the waves at different locations?